1. Field of the Invention
The present invention relates generally to fiber optic sensors and, more particularly, to a fiber optic sensor using a transmissive grating panel and a mirror, in which displacement resulting from a temperature change in the external environment or a behavioral change in an object to be measured is measured using a grating panel, a reflection mirror and an optical fiber, and then enables various measurements to be taken of the temperature change in the external environment and the behavioral change (displacement, pressure, vibration or acceleration, etc.) in the object on the basis of the measured displacement.
2. Description of the Related Art
Large structures, such as bridges, large buildings or power generating equipment, are very complicated, thus leading to accidents stemming from various causes. These accidents may result in enormous losses of life and property, and may cause great inconvenience in an industrial setting and in daily life. Hence, in order to maintain the safety of such large structures, it should be regularly checked whether repair or maintenance should be performed to prevent a disaster.
However, in the case of a poor electromagnetic environment, for example, a power plant or a railroad track, a great number of sensors are required and the length of electric wire for connecting the sensors to each other is considerably long, so that signal noise is serious when electromagnetic waves are not blocked. Thus, using a conventional electronic-based sensor is problematic.
Fiber optic sensors are also a sensing system used in smart structures. Since such a fiber optic sensor performs measurement using light it is operated without electromagnetic wave interference. Thus, the fiber optic sensor may be utilized even in an environment in which there are electromagnetic waves or during the operation of the structure. Further, the fiber optic sensor is highly sensitive and can measure defects in real time. Further, the fiber optic sensor is small in size and light in weight, so that when it is applied to a structure, the weight concentration effect is low, and in addition the fiber optic sensor is very small in diameter and is flexible, thus allowing a fiber optic sensor to be manufactured in a desired size. Furthermore, advantageously, the fiber optic sensor is resistant to environmental influences, such as corrosion, directed against the lifespan of the sensor, can be used over a wide range of operating temperatures due to excellent temperature characteristics, and can obtain information even over long distances, thus enabling monitoring without concern about the loss of life or experimental equipment even in dangerous environments.
Because of these advantages, extensive research into measuring physical quantities using the fiber optic sensor have been conducted until now. Further, extensive research is being conducted into using the fiber optic sensor as a sensor for monitoring the safety of a structure. However, as for an extrinsic fabry-perot interferometric (EFPI) sensor, the sensor utilizes an interference signal, so that a very small gap should be formed using a microscope, and it is complicated to process a signal because the interference signal is not in the form of a sine wave. Further, as for a fiber Bragg grating (FBG) sensor, a great deal of cost is required to construct a system and thus the sensor is not economical.
Conventionally, there is technology for measuring displacement, strain, acceleration, or the like using a grating pattern. This technology utilizes moire fringe that occurs when two grating patterns overlap each other. Thus, this technology requires two grating panels. Further, since this technology measures displacement, strain, acceleration, or the like using a transmission signal, two optical fibers serving as a light emitting part and a light receiving part should be provided in pairs. Hence, in the case of fabricating a sensor, optical fiber lines are extended to both sides, so that its structure becomes undesirably complicated.
Therefore, there is urgently needed research and development into a simple, economical and efficient sensor capable of being applied to a wide range of fields, for example, civil structures, building structures, power plants or railroad tracks which have a poor electromagnetic environment.